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Updated: Feb 22, 2026
Reconstitution of Msp1 Extraction Activity with Fully Purified Components
Published on: August 10, 2021
Lon protease: a novel mitochondrial matrix protein in the interconnection between drug-induced mitochondrial
Miriam Polo1,2, Fernando Alegre1,2, Angela B Moragrega1
1Departamento de Farmacología, Facultad de Medicina, Universitat de Valencia, Valencia, Spain.
Background And Purpose:
Mitochondria-associated membranes (MAMs) are specific endoplasmic reticulum (ER) domains that enable it to interact directly with mitochondria and mediate metabolic flow and Ca2+ transfer. A growing list of proteins have been identified as MAMs components, but how they are recruited and function during complex cell stress situations is still not understood, while the participation of mitochondrial matrix proteins is largely unrecognized.
Experimental Approach:
This work compares mitochondrial/ER contact during combined ER stress/mitochondrial dysfunction using a model of human hepatoma cells (Hep3B cell line) treated for 24 h with classic pharmacological inducers of ER stress (thapsigargin), mitochondrial dysfunction (carbonyl cyanide m-chlorophenyl hydrazone or rotenone) or both (the antiretroviral drug efavirenz used at clinically relevant concentrations).
Key Results:
Markers of mitochondrial dynamics (dynamin-related protein 1, optic atrophy 1 and mitofusin 2) were expressed differently with these stimuli, pointing to a specificity of combined ER/mitochondrial stress. Lon, a matrix protease involved in protein and mtDNA quality control, was up-regulated at mRNA and protein levels under all conditions. However, only efavirenz decreased the mitochondrial content of Lon while increasing its extramitochondrial presence and its localization to MAMs. This latter effect resulted in an enhanced mitochondria/ER interaction, as shown by co-immunoprecipitation experiments of MAMs protein partners and confocal microscopy imaging.
Conclusion And Implications:
A specific dual drug-induced mitochondria-ER effect enhances the MAMs content of Lon and its extramitochondrial expression. This is the first report of this phenomenon and suggests a novel MAMs-linked function of Lon protease.
Insights
Combined cell stress enhances the presence of Lon protease in mitochondria-associated membranes (MAMs), suggesting a new role for this matrix protease in regulating ER-mitochondria interactions.
Area of Science:
- Cell Biology
- Mitochondrial Dynamics
- Endoplasmic Reticulum Stress
Background:
- Mitochondria-associated membranes (MAMs) are crucial for ER-mitochondria communication, regulating metabolic flow and calcium transfer.
- The recruitment and function of MAMs proteins during complex cellular stress remain poorly understood.
- The role of mitochondrial matrix proteins in MAMs function is largely unrecognized.
Purpose of the Study:
- To investigate mitochondrial-ER contact dynamics under combined endoplasmic reticulum (ER) stress and mitochondrial dysfunction.
- To identify changes in MAMs composition and function during complex cellular stress.
- To explore the role of mitochondrial matrix proteins, specifically Lon protease, in ER-mitochondria crosstalk.
Main Methods:
- Utilized human hepatoma cells (Hep3B) treated with inducers of ER stress, mitochondrial dysfunction, or both.
- Analyzed expression of mitochondrial dynamics markers (DRP1, OPA1, MFN2) and Lon protease.
- Assessed Lon protease localization and mitochondria-ER interaction using co-immunoprecipitation and confocal microscopy.
Main Results:
- Combined ER and mitochondrial stress uniquely altered mitochondrial dynamics markers.
- Lon protease (matrix protease) was upregulated under all stress conditions.
- Efavirenz treatment specifically decreased mitochondrial Lon, increased its extramitochondrial presence, and enhanced its localization to MAMs, promoting mitochondria-ER interaction.
Conclusions:
- Dual drug-induced stress specifically enhances MAMs content and extramitochondrial expression of Lon protease.
- This study reports a novel MAMs-associated function for Lon protease.
- Lon protease may play a significant role in regulating ER-mitochondria crosstalk under complex stress conditions.
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